On line spectrophotometric method for the monitoring of colour removal processes
Résumé
A spectrophotometric method for the monitoring of a discoloration process, based on the calculation, in CIELAB colour space, of colour differences from visible spectra, has been developed. This procedure, simple and rapid, has been tested on standard azo dyes solutions (Trypan Blue and Red Remazol) and an industrial wastewater (paper industry). Advanced oxidation processes, vacuum UV photolysis and photo-oxidation in presence of hydrogen peroxide, have been studied. A discoloration yield (τ) has been defined from colour differences and a minimal value of this parameter (τmin) has been calculated according to the colourless zone (Standard Method 2120C). When τ value reaches τmin value, studied sample is colourless and the treatment process may be stopped. Moreover, the proposed procedure allows to detect any trouble shooting during the discoloration process (dτ/dt=0 when τ<τmin). The proposed procedure requires only the acquisition of UV–visible spectra versus time, is easy to implement on line and gives real time information.